Off-highway machines typically operate in areas having a relatively high concentration of dirt, dust and other debris in the surrounding atmospheric or ambient air. As an agricultural combine moves through a field, the normal operation of separating grain from material other than grain further complicates the air contamination problem in and about the entire machine.
Concern for operator comfort has led to development of increasingly sophisticated operator enclosures or cab regions on such machines. Modern cab designs are ergonomically configured to offer a comfortable and relatively clean atmosphere for the operator regardless of the outside environment.
It is well known in agricultural combines to provide a completely enclosed cab which takes in and filters outside air, heats or cools the air as ruined through an atmosphere control system, and circulates it within the cab as by means of a fan or pressurizing blower. Preferably, the air within the cab is maintained at a pressure slightly higher than atmospheric, so as to discourage the entry of dust or other contaminants through, for example, imperfectly sealed doors or windows. Some off-highway machines are provided with air inlets arranged toward a roof line of the enclosure. From the air inlet, air is drawn downwardly through a hollow rollover protective structure and then to a filter assembly.
Filter of the air from the intake becomes a formidable task, especially on agricultural combines. With agricultural combines, the entire environment immediately surrounding the combine is often saturated with dust and chaff. This load of debris in the inlet air can very quickly inundate the typical filtering systems (paper element inline filters) if fed directly from the outside environment to the filter without first precleaning a major portion of the undesirable matter out of the flow.
Accordingly, some off-highway machines utilize a precleaner apparatus disposed between the air intake and the filter. Most current commercially available precleaning units are not capable of sufficiently scrubbing the air of dust at the very low air flow rates required for this application. Moreover, the extremely dirty a that this application is subjected to has proven to overwhelm these devices and cause premature failure of their function. Accordingly, when the precleaner fails, the filter becomes plugged with dust and the effective cab pressurization is lost as the fan mounted within the cab enclosure is starved for inlet air. This results in dirty environmental air entering the cab through the aforementioned imperfectly sealed doors or windows, thus reducing the efficiency of the heating and air conditioning system and leading to extreme operator discomfort.
The remedy for this problem is to temporarily discontinue harvesting operations and take the necessary steps to service the air intake system. This requires the harvesting operation to cease. Thereafter, the filter must be cleaned to remove the built up debris from the inlet filter element and/or precleaning apparatus. This lost time and extra effort leads to operator dissatisfaction with the machine, and a desire for an alternative system that would not fall in these circumstances. Moreover, having to repeatedly clean the air intake system quickly leads to added downtime, reduced harvesting capacity and, thus, lost profits.
Thus, there is a need and a desire for an a intake system for an off-highway machine wherein it is possible to provide a very low air flow of precleaned air to the cab station while offering prolonged or extended operating times for the off-highway machine.